Contributed by Charlie
The only reason the game needed the expansion pak was because it contained a game-breaking bug. The game would randomly crash in the 4 meg version, but when they installed the expansion pak it worked perfectly. Rare couldn't find any other solution, so they bundled the expansion pak with the game, costing them a lot of money. They still don't know what caused the bug.

"There was a bug that caused the game to randomly crash that only occurred in the 4meg-only version ... and they couldn't find out what it was, so they had to shift with the memory card in it for free and it cost them a fortune." - Chris Marlow